The present invention provides an apparatus for measuring deformation of pipes and tubes. The apparatus is particularly useful in the field of chemical process technology where deformation may be caused by uneven heating of pipes and tubes. The invention also provides a method of measuring deformation of pipes and tubes.
In a thermal cracker unit where heat is used to convert saturated hydrocarbons into unsaturated hydrocarbons, the reaction mixture is generally passed through a furnace in metallic reactor tubes. Cracker units of this type are used in the process industry in order to provide a feedstock of unsaturated hydrocarbon for polymer production and other applications.
In order to heat the hydrocarbon reaction mixture in the reaction tubes of the cracker unit, a furnace is generally provided in a chamber containing a large number of cracker tubes which run parallel to one another through the chamber e.g. the pipes may run vertically from floor to ceiling of the chamber. However, the positioning of the furnace burners relative to the pipes has a tendency to cause hot spots in various parts of the chamber, and as a result the pipes are subject to temperature differentials. In particular, one side of the pipe i.e. the side closest to the heat source may be subject to higher temperatures than the other side, and this leads to a problem with circumferential creep i.e. deformation of the pipe around its circumference.
The working lifetime of the reaction tubes is shortened by this phenomenon, and hence the tubes need to be inspected regularly and replaced when they become deformed. Indeed, if circumferential creep is not detected in time and replacement tubes are inserted before the tubes fail, the cracker unit may have to be shut down immediately resulting in lost production time. At worst, this problem presents a serious safety risk.
Regular inspections of the cracker tubes are carried out when the cracker unit is shut down for routine maintenance and repair. However the existing methods of measuring the deformation of cracker tubes are time consuming and inefficient. Visual inspection and manual measurement of pipe diameter/circumference is often inconvenient because the pipes are close to one another, impeding access to the pipes. Furthermore, scaffolding may be necessary in large chambers in order to reach the top part of the pipes.
Japanese Patent Application No. 08063873 of Japan Energy discloses an apparatus for inspecting pipelines by using a radiation source that is moved along the pipes to detect corrosion. This apparatus is however designed to detect corrosion in pipes, rather than circumferential deformation. Furthermore, the method was developed to enable inspection of pipes without removing a heat insulation layer around the pipe. This renders the apparatus unnecessarily complex for use in cracker units in which the pipes are not insulated.
Japanese Patent Application No. 11-211700 discloses an apparatus that uses ultrasound to detect creep damage in pipes by determining the maximum roughness of the pipe. The apparatus transmits a sound wave into the pipe such that it passes through the pipe to a circumferentially offset receiving probe. A further probe detects the echoes of reflected waves. However this apparatus is disadvantageous because as well as requiring a source of ultrasound and detector probes, comparatively complex calibration and analysis of the output data is required.
It will therefore be seen that the prior art does not provide a cost-effective and efficient way to measure deformation in pipes such as those found in petroleum crackers.